This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2003-51112, filed on Jul. 24, 2003, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electrophotographic printer. More particularly, the present invention relates to an electrophotographic printer with a simplified structure that facilitates further reduction in the size of the printer.
2. Description of the Related Art
Generally, electrophotographic printers print monochromatic or color images by scanning light onto a photosensitive medium charged to a predetermined potential to form an electrostatic latent image, developing the electrostatic image with toners of predetermined colors using a developer, and transferring and recording the developed image onto a physical recording medium such as a sheet of paper.
Electrophotographic printers can be divided into liquid electrophotographic printers and dry-type electrophotographic printers according to the type of developer. A liquid electrophotographic printer uses a developer in which a powder toner is mixed with a liquid carrier. A dry-type electrophotographic printer uses a two-component developer including a powder carrier and a toner, or a single-component developer including a toner only. Hereinafter, the dry-type electrophotographic printer will be described, and the developer may be referred to as toner.
In order to print a full-color image, different colored toners, such as yellow (Y), magenta (M), cyan (C), and black (K) colors are required. Thus, four developing devices that each develop one of the four color toners are required. To form a full-color image, there is a single path method, in which when a transfer substance passes through photosensitive substances, on which four color images are formed, the color images are sequentially transferred, and there is a multi-path method, in which when the transfer substance passes through the photosensitive substances, the image is transferred from only one photosensitive substance and the process is repeated to form the image. In both methods, the four developing devices are generally required.
When a color image is printed using the multi-path method, the processing time is four times longer than when printing a monochromatic image, however, the structure of the printer is simple. When a color image is printed using the single-path method, the printing time is the same as when printing a monochromatic image, and thus color printing can be performed at a high speed.
FIG. 1 is a cross-section of a conventional electrophotographic image forming apparatus using the single-path method, and FIG. 2 is a cross-section of a developing device of the apparatus shown in FIG. 1.
Referring to FIG. 1, the image forming apparatus includes a light scan unit 20 that scans light onto four photosensitive drums 10, which are charged to a predetermined electric potential, to form an electrostatic latent image, four developing devices 30 that develop the electrostatic latent image with four color toners (Y, M, C, and K) to form toner images on the photosensitive drums 10, a feeding belt 40 that conveys a sheet of paper onto which the toner images of four colors formed on the photosensitive drums 10 are transferred sequentially, and a fuser 50 that fuses the toner image onto the paper by heating and pressing the paper onto which the toner image has been transferred. A paper feeding cassette 60 that feeds the paper (S) is installed to be inserted/removed from a main body of the image forming apparatus. The photosensitive drums 10 are integrally installed on respective developing devices 30, and the developing devices 30 including the photosensitive drums 10 are vertically disposed to perform a color printing operation according to the single-path method. This contributes to making the image forming apparatus compact.
Referring to FIG. 2, which shows one of the developing devices 30 of the apparatus of FIG. 1, the photosensitive drum 10 is integrally installed on the developing device 30. The developing device 30 includes the photosensitive drum 10, a charging roller 31 that charges the photosensitive drum to a predetermined electric potential, a developing roller 32 that develops the electrostatic latent image on the photosensitive drum 10, and a plurality of agitators 33 that mix and supply the toner in the developing device 30 to the developing roller 32. Reference numeral 34 denotes a case of the developing device 30, reference numeral 34a denotes an opening through which a laser beam passes to form the electrostatic latent image on the photosensitive drum 10, and reference numeral 35 denotes a cleaning roller for removing toner remaining on the photosensitive drum 10.
The developing device 30 further includes a cover 71 that protects the photosensitive drum 10 from light and dust when the printer is opened to change a photosensitive drum 10 or clear a paper jam. Both ends of the cover 71 are connected to shafts 72, and end portions of the shafts 72 are connected to levers 73. The shaft 72 and the lever 73 are coupled by a hinge 74, and the shaft 72 is connected to an spring 75. Therefore, when the lever 73 rotates in the counterclockwise direction, the shaft 72 and the cover 71 also rotate in the counterclockwise direction to expose some part of the photosensitive drum 10, so that the toner images can be transferred onto the paper placed on a paper feeding path. Also, when the lever 73 is released, the shaft 72 is drawn back to its original position by the spring 75 so that the cover 71 and the lever 73 rotate in the clockwise direction and the cover 71 protects the surface of the photosensitive drum 10.
However, in the color printer using the single-path method, in which the photosensitive drums 10 are vertically arranged using the four developing devices 30 (toner cartridges), a cover unit for protecting the photosensitive drum 10 is required for every toner cartridge. This takes up a lot of space and is a limitation to making the color printer compact.